1. Field of the Invention
The present invention relates to new polymers and use of such polymers as a resin component for photoresist compositions, particularly chemically-amplified positive-acting photoresist compositions. Polymers of the invention comprise groups that can generate multiple anions or acidic groups, and/or generate substantially no volatile species during lithographic processing.
2. Background
Photoresists are photosensitive films used for the transfer of images to a substrate. A coating layer of a photoresist is formed on a substrate and the photoresist layer is then exposed through a photomask to a source of activating radiation. The photomask has areas that are opaque to activating radiation and other areas that are transparent to activating radiation. Exposure to activating radiation provides a photoinduced chemical transformation of the photoresist coating to thereby transfer the pattern of the photomask to the photoresist-coated substrate. Following exposure, the photoresist is developed to provide a relief image that permits selective processing of a substrate.
A photoresist can be either positive-acting or negative-acting. For most negative-acting photoresists, those coating layer portions that are exposed to activating radiation polymerize or crosslink in a reaction between a photoactive compound and polymerizable reagents of the photoresist composition. Consequently, the exposed coating portions are rendered less soluble in a developer solution than unexposed portions. For a positive-acting photoresist, exposed portions are rendered more soluble in a developer solution while areas not exposed remain comparatively less developer soluble. In general, photoresist compositions comprise at least a resin binder component and a photoactive agent.
More recently, chemically-amplified-type resists have been increasingly employed, particularly for formation of sub-micron images and other high performance applications. Such photoresists may be negative-acting or positive-acting and generally include many crosslinking events (in the case of a negative-acting resist) or deprotection reactions (in the case of a positive-acting resist) per unit of photogenerated acid. In the case of positive chemically-amplified resists, certain cationic photoinitiators have been used to induce cleavage of certain xe2x80x9cblockingxe2x80x9d groups pendant from a photoresist binder, or cleavage of certain groups that comprise a photoresist binder backbone. See, for example, U.S. Pat. Nos. 5,075,199; 4,968,581; 4,883,740; 4,810,613; and 4,491,628, and Canadian Patent Application 2,001,384. Upon cleavage of the blocking group through exposure of a coating layer of such a resist, a polar functional group is formed, e.g., carboxyl or imide, which results in different solubility characteristics in exposed and unexposed areas of the resist coating layer. See also R. D. Allen et al., Proceedings of SPIE, 2724:334-343 (1996); and P. Trefonas et al. Proceedings of the 11th International Conference on Photopolymers (Soc. Of Plastics Engineers), pp 44-58 (Oct. 6, 1997).
While currently available photoresists are suitable for many applications, current resists also can exhibit significant shortcomings, particularly in high performance applications such as formation of highly resolved sub-half micron and sub-quarter micron features.
The present invention provides novel polymers and photoresist compositions that comprise a photoactive component and such polymers as a resin component.
In a first aspect, polymers of the invention in general comprise a photoacid-labile unit (sometimes referred to as a xe2x80x9cblocking groupxe2x80x9d) that can generate multiple anions or acidic groups such as hydroxy (particularly phenolic) preferably from a single photoacid-induced polymer deprotection reaction.
In a further aspect, polymers of the invention comprise a photoacid-labile unit (i.e. blocking group) generate substantially or essentially no volatile species (e.g. boiling point less than about 180xc2x0 C. or 200xc2x0 C.) species during a photoacid-induced deprotection reaction of the polymer to thereby avoid undesired outgassing and/or shrinkage of a resist coating layer containing a polymer of the invention.
In particularly preferred aspects of the invention, polymers are provided that combine both of the above aspects, i.e. the polymers contain blocking groups that can generate multiple anions or acid groups preferably from a single photoacid-induced polymer deprotection reaction, and those blocking groups also generate essentially no volatile species (e.g. boiling point less than about 180xc2x0 C. or 200xc2x0 C.) species during a photoacid-induced deprotection reaction of the polymer.
Particularly preferred polymers of the invention comprise one or more acetal, ketal and/or ortho esters photoacid-labile groups (blocking groups) that preferably can generate multiple anions. Unless otherwise specified, references herein to acetal groups are inclusive of both acetal, ketal and ortho ester groups.
A suitable acetal precursor compound or other suitable blocking group precursor may be grafted onto a preformed polymer to provide a polymer with photoacid labile acetal group. Upon exposure to photoacid, the acetal unit is cleaved or deblocked, which can provide an anion or acidic group on the polymer. Moreover, by appropriate selection of the acetal precursor compound, after deblocking, the cleavage product itself can generate a further anion or acidic group.
The generation of multiple anions or acid groups from a single deblocking reaction can provide photoresist relief images of enhanced contrast and resolution. The use of blocking groups that generate substantially or essentially no volatile species avoid undesired outgassing and shrinkage of a resist coating layer containing a polymer of the invention. Such outgassing and shrinkage can compromise resolution of an image patterned in the resist layer as well as damage or at least interfere with the performance of imaging equipment. For example, volatile products of a deblocking reaction can condense on lenses of a stepper or other imaging equipment.
Photoresists of the invention contain a photoactive component, typically a photoacid generator compound, and a resin component that comprises a polymer of the invention. Photoresists of the invention can be imaged with a variety of activating radiation, depending on the photoactive component that is employed. Generally preferred will be deep UV wavelengths (recognized as less than about 300 nm), including 248 nm, and sub-200 nm wavelengths such as 193 nm and 157 nm. Other useful exposure radiation includes E-beam, X-ray, EUV, and ion projection lithography (IPL).
The invention also provides methods for forming relief images, including methods for forming a highly resolved relief image such as a pattern of lines where each line has essentially vertical sidewalls and a line width of about 0.40 microns or less, or even about 0.25 microns or less. The invention further provides articles of manufacture comprising substrates such as a microelectronic wafer or a liquid crystal display or other flat panel display substrate having coated thereon the photoresists and relief images of the invention. Other aspects of the invention are disclosed infra.